Wide modulation range reheat fuel system



March 21, 1961 WIDE MODULATION RANGE REHEAT FUEL SYSTEM J. W. VDOVIAK Filed June 6, 1955 United States Patent The present invention relates to a wide modulation range reheat fuel system and, more particularly, to a reheat fuel system which prevents temperature surge when the afterburner is ignited.

' A problem which exists with present day after-burners is the considerable temperature surge and associated thrust jump which occurs when the afterburner is ignited. Referring to fundamental combustion theory, it is known that a fuel-air ratio of less than approximately .03 will not support stable or eflicient combustion at normal pressures. Therefore, to ignite a conventional afterburner the reheat fuel flow must :be increased to a point corresponding to .03 whereupon a temperature surge of approximately 1500 occurs. On the present and future high speed aircraft this surge and thrust jump cannot be toler: ated from either an operationalor structural standpoint. To overcome this problem the present invention provides two fuel systems linked together automatically. One fuel system injects fuel locally just ahead of the flameholder. This provides a local combustible fuel-air ratio behind each gutter, although the overall average fuel-air ratio in the afterburner is too lean to ignite. This system operates from light off up to a fuel flow corresponding to a-fuel-air ratio of approximately .03 at which point fuel is transferred to a second fuel distribution system positioned upstream of the gutters. The local injecting system has high performance characteristics at low fuel-air ratios whereas the second, or uniform, injecting system has like characteristics at high fuel-air ratios. By proper selection of the transfer point, the operation of the afterburner may be set to follow the maximum envelope of both systems. 'In addition, at severe operating conditions, the local system may be operated simultaneously with the uniform system to achieve combustion performance superior to that obtained by using the uniform system alone.

An object of the presentinvention is to provide a re heatfuel system operable. over a wide range of average burner fuel-air ratios. p

Another object is to provide a reheat fuel system operable at very low average burner fuel-air ratios.

An additional object is the provision of a reheat fuel system having a wide range of modulation.

A further object is the provision of a wide modulation range reheat fuel system which reduces temperature surge at ignition to a minimum.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with accompanying drawing wherein:

A reheat fuel system according to the present invention is shown in schematic form.

Referring more particularly to the drawing, a complete reheat fuel supply system includes fuel tank 11, fuel pump 12, metering valve 13, pressure selector valve 14, pilots throttle lever 15, system selector valve 16, a local distribution system 17 and a uniform distribution system 18. The metering valve 13 is connected into the fuel supply line 19 and includes an outer casing 21 in which is positioned an axially movable member 22 and an overlapping rotatable member 23. Members 22 and 23 are each provided with openings which overlap to define the fuel metering port 24. The throttle lever 15 is operatively connected to the rotatable member 23 as by rod 25, link 26, shaft 27, lbevel gears 28 and 29 and shaft 31. The pressure selector valve 14 is connected across pump 12 as by lines 32 and 33 and includes a pair of movable pistons 34 and 35 secured to the piston rod '36. The piston rod 36 is operatively connected to the pilots throttle lever as by link 37, shaft 38, link 39 and rod 25. The system selector valve 16 is connected to valve 14 by line 42 and to the main fuel line 19 ahead of the pump 12 by line 41. The system selector valve 16 includes an outer casing in which are positioned a pair of movable pistons 43 and 44 which are secured together by shaft 45, the pistons being biased in a local position by the spring 46. An adjustable stop means 47 is provided to limit the movement of the pistons 43 and 44 against the action of the pressure in line v42. The local fuel distribution system 17 is connected to the selector valve 16 by lead 48 and includes a spring loaded relief valve 49 and one or more concentric ring manifolds 51 mounted adjacent, i.e., immediately upstream of the flameholder gutters 53. The

. relief valve and the manifolds are connected as by the lines 54 and 55. The uniform fuel distribution system 18 spraybars being connected to the relief valve 57 by the lines 61 and 62.

In the operation of the present invention, fuel is pumped from the tank 11 through the main fuel line 19 through the metering valve 13 to the system selector valve 16. Boost pressure and pump pressures are applied to the pressure selector valve 14 through the lines 32 and 33 respectively. When the throttle is in the light-off position,

as shown, the piston 35 closes the port connected to the line 33 allowing the boost pressure in line 32 to be transmitted through the valve to the line 42, Where it is applied to one side of the piston 43. The line 41 also supplies boost pressure to the opposite end of selector valve 16 where it is applied to one side of the piston 44, thus balancing the pressure applied to the piston 43 and allow ing the spring 46 to position the two pistons such that the port to theline 48 is open. Fuel is supplied by the main fuel line 19 to the system selector valve 16 where it is directed through the line 48 to the local distribution system 17. At light-off, the relief valve 49 directs the fuel flow from the line 48 through the line 54 to one set of concentric ring manifolds 51 where it is injected into the air stream immediately behind the gutters 53. As throttle lever 15 is advanced, the metering orifice 24 is enlarged allowing a greater fuel flow through the fuel line 19 to the selector valve 16. This increased fuel flow is delivered through the line 48 and applied to the relief valve 49 which releases at a certain desired pressure allowing fuel to flow through the line 55 and be applied to the rings of the other manifold, which will increase the local fuel/air ratio behind each of the gutters 53. When the throttle lever is advanced, the piston rod 36 is also moved to adjust the position of the pistons 34 and 35 until the piston 34 covers the port connected to line 32 allowing pump pressure to be supplied through the lead 33 to the line 42. The pump pressure supplied to the valve 16 is applied to the piston 43 and is of sufiicient magnitude to overcome the combined effects of the booster pressure and the spring 46. Pistons 43 and 44 are thereby positioned to close the port connected to the lead 48 and open the port connected to the lead 56 allowing fuel to be supplied through line 56 to the relief valve 57 which directs the entire fuel fiow through line 61 to one of the spraybars 58. As the throttle lever is advanced further, the metering orifice 24 is enlarged and the fuel flow delivered through the main fuel line 19 and line 56 is increased to the point where relief valve 57 allows the fuel to also be applied through line 62 to the remaining spraybars. The adjustable stop 47 can be used to limit the travel of the pistons 43 and 44 such that under high thrust conditions the port connected to the line 48 is not completely closed, thus allowing a small percentage of the total fuel to be injected through the local fuel distribution system while the remainder of the fuel is injected through the uniform distribution system.

The local distribution system has sufficient capacity to satisfy fuel flow requirements from light-off to the augmentation corresponding to an average fuel-air ratio of .03. The transfer from the local distribution system to the uniform distribution system is therefore made at approximately this point, thus allowing operation at full augmentation on either the uniform distribution system alone or combined with the local system as set forth above.

While the local system and the uniform system are illustrated as including a plurality of ring manifolds and spraybars, respectively, it should be understood that either or both systems can be constructed with but a single fuel injection means. In addition, the ring manifolds are shown as mounted ahead of the fiameholder gutters but it is contemplated that in certain instances it may be desira'ble to mount the manifold in the gutters or to make them integral therewith.

Obviously, many modifications and variations of the present invention are possible in the light of the above teaching. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What I claim is:

1. In a turbojet engine including a tail pipe having a fiameholder mounted therein, said fiameholder including a plurality of concentric members, a reheat fuel system comprising: a throttle control selector; a system selector connected to said throttle control selector; a first fuel dis tribution system connected to said system selector, said first system including fuel injection means mounted in said tail pipe and attached to said fiameholder members, and a uniform fuel distribution system connected to said system selector, said uniform system including fuel injection means mounted in said tail pipe upstream of said fiameholder, said system selector controlling the flow of fuel to the distribution systems in response to movements of the throttle control selector whereby at low throttle settings fuel is delivered through the first system and injected in the immediate vicinity of the fiameholder, and at high throttle settings fuel is delivered through the uniform system and injected upstream of the fiameholder,

said first injection means supplying fuel to each of said fiameholder members at said low throttle settings.

2. In a turbojet engine including a tail pipe having a fiameholder mounted therein, said fiameholder including a plurality of concentric gutters disposed transversely of said tailpipe, a reheat fuel system comprising: first fuel injection means mounted within said tail pipe adjacent each of the fiameholder gutters; second fuel injection means mounted within the tail pipe upstream of the fiameholder; a selector valve operatively connected to each of said first and second fuel injection means; and a throttle control selector operatively connected to said selector valve, said selector valve controlling the fiow of fuel to the injection means in response to movements of the control selector, to inject fuel only through the first means at low throttle settings, and through only the second means at high throttle settings, said first injection means supplying fuel to each of said gutters at said low throttle settings.

3. In a turbojet engine including a tail pipe having a fiameholder mounted therein, said fiameholder including a plurality of concentric gutters disposed transversely of said tailpipe, a reheat fuel system comprising: a plurality of fuel ring manifolds mounted within the tail pipe for injecting fuel in the immediate vicinity of each of said fiameholder gutters; at least one spray bar mounted within the tail pipe for injecting fuel uniformly upstream of the flameholders; a selector valve operatively connected to References Cited in the file of this patent UNITED STATES PATENTS 2,508,420 Redding May 23, 1950 2,780,915 Karen Feb. 12, 1957 2,793,495 Karcher May 28, 1957 FOREIGN PATENTS 1,075,220 France Apr. 14, 1954 577,062 Great Britain May 2, 1946 684,244 Great Britain Dec. 17, 1952 OTHER REFERENCES Third Symposium on Combustion, Flame and Exp1osion Phenomena; under auspices of The Standing Committee on Combustion Symposia; pages 44-68: Williams & Wilkins Co., Baltimore, Maryland (1949). 

